Colorectal cancer (CRC) is the third most commonly diagnosed cancer and the third leading cause of cancer deaths among Veterans. Multiple screening modalities are available and have been shown to decrease the incidence and mortality from CRC, but the Veterans Health Administration's (VHA) capacity to provide this screening is strained. For example, although the VHA aims to complete follow up of positive fecal occult blood tests with colonoscopy within 60 days, the average waiting time for colonoscopy is more than three times that goal. The most commonly cited barrier to meeting this goal involves capacity constraints in endoscopy. The VHA has addressed this challenge by hiring additional staff and outsourcing endoscopic care to non-VHA providers, at great expense to the organization. A complementary and more cost-effective approach to increasing the supply of staff is to optimize the efficiency of existing resources to absorb additional demand. Because of its importance to providing quality and timely care to Veterans, improving health care efficiency and productivity is a major initiative in the VHA strategic plan. Moreover, timeliness and efficiency of care, as defined by the Institute of Medicine, are critical dimensions of health care quality. A number of methodologies have been used to improve efficiency in health care delivery including six sigma and lean. Discrete event simulation (DES) is an operations research methodology that is not routinely used in VHA system redesign efforts but can be applied to improve patient flow and efficiency of clinic operations. DES has been well established and validated as a business intelligence tool in the manufacturing sector and has been shown to be effective in a number of healthcare contexts. However, while there have been numerous publications on the creation of DES models in healthcare, there has been a dearth of literature on their implementation and use. The proposed research aims to bridge this limitation and develop generalizable knowledge regarding how DES can be used most effectively to improve efficiency in GI endoscopy and how to facilitate broader implementation of his approach within the VHA to improve capacity of CRC screening. To accomplish this goal, this project has three aims: 1) Utilize DES modeling to evaluate opportunities for increased efficiency of the Durham VA GI Endoscopy Unit; 2) Conduct a formative evaluation to understand the barriers and facilitators to implementing simulation-guided systems redesign with the VHA; and 3) Pilot the use of simulation modeling to guide systems redesign activities in the endoscopy unit at the Durham VA Medical Center. The Promoting Action on Research Implementation in Health Services (PARIHS) conceptual framework will guide the development and testing of the simulation- guided intervention and serve as the foundation for a subsequent Merit Review application. The proposed career development program will result in a simulation-based intervention to expand the screening capacity of the VHA through improved endoscopy unit efficiency and will prepare me to conduct independent research, guided by implementation theory, on the dissemination of simulation-guided systems redesign more broadly within the VHA. This research program aligns with the strategic goals of HSR&D and the eHealth QUERI and can strengthen the important link between clinical care, healthcare systems engineering and systems redesign.